The present invention relates to the recovery of tobacco from a mixture of tobacco and non-tobacco particles and, in particular, to methods and apparatus for separating tobacco particles from soil particles in a stemmery discard.
In an effort to recover as much of the useful component of tobacco leaves as possible, the leaves are treated in stemmeries which remove leaf lamina from the stems by a series of threshing stages. This results in the production of tobacco fines or particles of a relatively wide range of small sizes, along with appreciable amounts of non-tobacco particles, especially soil particles such as dirt and sand which accompanied the stems to the stemmery. The mixture of tobacco particles, stems, and soil particles is subjected to a series of separation steps in the stemmery, usually involving vibratory reciprocal screens, in an effort to recover the larger tobacco particles, which can be used in the manufacture of tobacco products.
The residue of the final separating step comprises a mixture of very small tobacco particles and a large amount of soil particles. That mixture is unsuitable for use in the manufacture of tobacco products, due to the excessive contamination by soil particles. In particular, the abrasiveness of the soil particles, especially sand, would damage the tobacco processing equipment. Consequently, that mixture is discarded and sent to landfill.
It would, therefore, be desirable to recover tobacco particles from that stemmery discard, not simply to reduce tobacco waste and slow the rate of depletion of landfill space. However, the difficulties involved in recovering useful tobacco (i.e., tobacco accompanied by only a small amount of soil particles, such as less than twenty percent, and most preferably less than eight percent by weight) from stemmery discard has discouraged such recovery efforts. Among the reasons for these difficulties is the smallness of the tobacco particles which are difficult to separate from soil particles and which tend to clog or "blind" screen type separators. Also, since the tobacco particles, although small, occupy a relatively wide range of sizes and shapes, they are difficult to separate on the basis of density by conventional gravity-type separators.
Therefore, it would be desirable if an efficient and effective way could be found to recover tobacco from a stemmery discard in order to minimize both the amount of tobacco waste and the rate of depletion of landfill space.